Process for manufacture of improved lubricating oils



Patented Aug. 29, 1944 trap srAr PROCESS FOR MANUFACTURE IMPROVED LUBRICATING OILS Robert W. Henry, Bartl esvllle, 0111s., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application October Serial No. 414,380

2 Claims.

This invention relates to lubricating oil and more particularly to a processof making an improved lubricating oil.

It has long been known that the presence of sulfur in some forms in lubricating oils is beneflelal in reducing wear, reducing oxidation in the presence of metals by inhibiting the catalytic action of such metals, and in reducing corrosion, especiallycorrosion of certain bearing metal alloys such as copper-lead, cadmium-silver, cadmiumnickel, etc. .However, lubricating oil distillates from high sulfur bearing crude oils ordinarily are of the low viscosity index, so-called naphthenic,

type which are relatively unsuited to many high duty engine services. The industry has attempted to manufacture high viscosity index oils from such naphthenic or coastal type distillates, as by solvent extraction, but in such case excessive extraction is necessary with consequent very low yields and high cost, and the resulting oils exhibit undesirable properties due to the excessive extraction, These undesirable properties include lack-of stability to oxidation, lack of desired film strength, and tendency to oorrosiveness, due to removal, in the excessive extraction, of natural inhibitors to oxidation and corrosion, and of components contributing to high film strength.

These desirable inhibiting and high film strength components which are removed to an objectionable degree by'the excessiveness required in the extraction in order to give the desired increase in viscosity index may or may not be of the sulfur bearing type.

Also, attempts have been made to secure the advantages of presence of certain sulfur compounds in lubricating oils by heating the finished refined oils with elemental sulfur whereby a very little sulfur goes into permanent solution and a larger amount reacts chemically with the oil, the resulting compounds being soluble in the oil. In this chemical reaction, numerous diverse and complex sulfur compounds tend to form in the lubricant, with formation and evolution of hydrogen sulfide. Control of this reaction to give a uniform product having the desired properties without also adding deleterious properties has been found to be impossible, and the product contains undesirable sulfur compounds in an excessive amount.

Another method of securing the desirable prop erties accompanying the presence of certain sulfur compounds-is to add a synthetic organic sulfur compound to the refined lubricating oil. This method involves the objections that the cost of such desirable synthetic sulfur compoundsis excessively high and moreover the results are not entirely satisfactory.

The principal object of the present invention I is to provide a processenabling attainment of the advantages of sulfur containing lubricating oil of high viscosity index without the presence of deleterious sulfur compounds and decomposition products.

Another object is to provide a novel process of preparing an improved lubricating oil from a high viscosity index mixed base lubricating oil stock of extremely low sulfur content.

Another object is to prepare a lubricating oil of improved characteristics from an Oklahoma City type lubricating oil stock. I

Another object is to prepare an improved sulfur-containing lubricating oil in improved yield from a mixed base stock.

Another object is to provide a process of introducing sulfur in desirable combined form into a mixed base crude in an extremely efllcient manner involving a minimum loss of sulfur in the form of hydrogen sulfide and in the form of undesirable sulfur compounds which must be re- 25 moved from the oil and disposed of.

Numerous other objects will hereinafter appear. In proceeding in accordance with my invention,

I may add sulfur to anunrefined lubricating oil stock of high viscosity index,.i. e., at least 75, but 6 of low sulfur content, 1. e., not more than 0.3 per cent by weight of sulfur, by mixing with the unrefined oil elemental sulfur and mildly heating.

The heating is controlled so as to put all or substantially all of the'added sulfur, amounting to 35 from about 0.5 per cent to about 4.0 per cent by weight of sulfur based on the weight of the stock,

into the raw oil in'combined form without excessive formation of deleterious products and without evolution of hydrogen sulfide or appreciable formation thereof. To this end the temperature should beat least 200 F. and less than 250 FL,

a temperature of 240 F. being preferred. The

combination of the oil stock and the sulfur may be in a separate step, or in conjunction with a 45 step in the usual refining procesafor example in a pipe-coll heater preliminary to solvent extraction. a

The resulting raw stock containing the combined. sulfur is then refined by solvent extraction. 5 It has been found that the commercial selective extraction solvents, such as phenol, cresol, furfural, beta dichloroethyl ether, nitrobenzene, aniline, liquid sulfur dioxide preferably in conjunction with benzene, etc., remove only the del- 55 eterious sulfur compounds, together with any decomposition products, along with the components which would normally be removed by such solvents when applied to the unrefined oil stock which had not been treated with sulfur in the manner Just described. The solvent extraction leaves the desirable sulfur compounds in the raffinate oil.

Thus a high viscosity index lubricating oil having the advantages of desired sulfur content without the disadvantages of the presence, of undesirable unstable, complex sulfur compound of the more reactive type, is formed.

Preferably the solvent used in the extraction step of my process is polar, since it has been found that extraction with a polar solvent removes the more polar sulfur compounds, leaving in the raflinate the relatively non-polar sulfur compound. Examples of the more polar solvents which are preferred are phenol, cresol, furfural, nitrobenzene, aniline, liquid sulfur dioxide, nitromethane, and the like. While the exact composition and structural configuration of the desirable sulfur compounds introduced into the stock by my process is not known, they are known to be relatively non-polar and are believed to be of the sulfur-in-the-ring type with long parafiin chains also attached to the ring. These compounds impart to the refined oil the properties of high film strength, increased stability to oxidation, and decreased corrosive tendency.

My invention is particularly applicable to lubricating oil stock typified by that derived from Oklahoma City crude oil. Such unrefined stock has a viscosity index of 75-80 and a sulfur content of' from 0.2 per cent to 0.3 per cent by weight. However my invention is also applicable to unrefined stocks of even higher V. I. and even lower sulfur content such as stocks derived from Pennsylvania crude, which are greatly benefited by treatment in accordance with the present' invention. In general unrefined stocks from Pennsylvania crudehave a V. I. of at least 100 and a sulfur content of less than 0.05 per cent.

By employing a low temperature in efiecting reaction with the sulfur, my process avoids the formation of objectionable hydrogen sulfide which involves ineflicient utilization of sulfur and interferes with the subsequent selective solvent extraction. Use of a low temperature also makes my process economical and prevents undue decomposition and side reactions.

My process enables a very efllcient utilization of the added sulfur, allowing at least 80 per cent and generally more of the added sulfur to remain in the finished oil in the form of desirable sulfur compounds. In other words, the deleterious sulfur compounds removable in the solvent refining step are not formed in the heating step (in amount corresponding to more than about 20 per cent of the added sulfur. Thus it is not necessary to employ an excess of sulfur, although such an excess may of course be initially added if it be desired, the unreacted sulfur being removed either by settling and filtration, centrifuging, or the like after the heating step, or by the solvent used in the extraction step. The use of from about 0.625 per cent to about 5.0 per cent of and frequently above 95 per cent by volume based on the volume of the original deasphalted, dewaxed, but otherwise unrefined, stock. The possibility of such high yields may be attributed to the very high V. I. of the original stock, to the relatively high percentage of desirable sulfur compounds formed in the process, and to the flexibility of control of th process. If desired, however, the process may be so carried out that lower yields are obtained, higher yields being sacrificed for other considerations. It will of course be understood that the actual yield will additionally depend upon a variety of controllable factors in the solvent extraction step, among which are the solvent employed, ratio of solvent to the reaction product from the heating step, temperature of extraction, length of contact, mode of effecting extraction, etc. 7

Example A deasphalted dewaxed Oklahoma City lubricating oil stock having a V, I. of 80 and a sulfur content of 0.27 per cent was admixed with 1 per cent of its weight of sulfur. The mixture was heated to 240 F. for three hours when all of the sulfur had combined with the oil. The treated stock was then cooled to 140 F. and extracted in a continuous countercurrent tower with 300 per cent by volume of furfural. The rafllnate had a viscosity index of 81 and a sulfur content of 0.83 per cent. It exhibited much higher film strength, resistance to oxidation, and freedom from corrosiveness than the untreated raw stock solvent extracted in the same manner. The yield of the rafllnate was 96% based on the volume of the original raw stock.

From the foregoing it will be seen that the process of the present invention provides a concosity index stock which is very low in natural sulfur and of relatively parafiinic type, i. e., either the more paraffinic of the Mid-Continent stocks initially added sulfur, with complete combination, and with 20 per cent removal in the extraction step, or 80 per cent utilization, introduces the desired 0.5 to 4.0 per cent into the oil.

In addition to effecting improved utilization of sulfur, my process enable'sthe attainment of a very high yield of refined oil based on the original stock. This yield may be above 90 per cent or the highly parafllnic Pennsylvania stocks. It will further be seen that the process involves relatively little waste or loss of sulfur, the small amount of sulfur employed serving to very effectively improve the characteristics of the treated oil by simultaneously effecting introduction of desirable sulfur compounds into the oil and the formation and removal of the undesirable sulfur compounds from the oil. Anotheradv'antage is the excellent yield of very high quality motor oil made possible by the present invention. Another advantage is the low cost of the process. In addition by eliminating the necessity for employing fatty oils the process eflects further economies. Yet other advantages are the elimination of the formation of hydrogen sulfide, and theme of low temperatures in the sulfurizing step. Numerous other advantages will appear to those skilled in the arts.

It will be understood that numerous changes may be made without departing from the spirit of my invention which is to be taken as limited only by the appended claims. For example, the heating step may be conducted under elevated pressures if desired.

I claim:

1. The process of refining a Mid-Continent lubricating 011 stock having a viscosity index of at least and a sulfur content below approximately 0.3% by weight which comprises incorporating into the oil stock approximately 0.625% to 5% by weight of elementary sulfur, heating the reremove any deleterious sulfur compounds and preciable formation or hydrogen sulfide, and soiaasaess suiting mixture to a temperature between the incorporating into said all stock approximately approximate limits of 200 to 250 F. for a suiii-- 0.625% to 5% by weight of elementary sulfur. cient length of time as to cause substantially all heating the resulting mixture to a temperature of the added sulfur to combine with the oil stock of approximately 240 F. for a sumcient length without appreciable icrmation of hydrogen suls. of time as to cause substantially all oi the added iide, and solvent extracting the so treated oil to suliur to combine with the oil stock without apother undesirable components and leave a refined vent extracting the so treated oil to remove any lubricating 011 stock containing sulfur in the form deleterious sulfur compounds and other undesiroi desirable sulfur compounds and comprising at I able components and leave a refined lubricating least 95% by volume 01' the original oil stock, the oil stock containing sulfur in the form 0! desirextract containing not more than 20% ot the able sulfur compounds and comprising atl added sulfur in the form 01' said deleterious 8111- 95% by volume oi the original oil stock. the exi'ur compounds. tract not more than 20% of the added 2. The process of refining an Oklahoma City it sulfur in the form oi said deleterious sulfur comunreiined lubricating oil stock having a viscosity pounds. index or at least 75 and a sulfur content below ROBmT W. 

